The present invention relates generally to motor vehicle fuel filling systems and, more particularly, to a fuel and vapor control system for controlling the release of evaporative and running loss fuel vapors into the atmosphere.
In view of stringent environmental and safety regulations which significantly restrict the emission of non-combusted hydrocarbons (i.e. fuel vapors) into the atmosphere, emission control systems are incorporated into modern motor vehicles. These systems are adapted to prevent or substantially minimize the release of fuel vapors from the fuel tank and/or the fuel intake system of an internal combustion engine. Most conventional emission control systems use a vapor capture device, such as an activated charcoal canister, for absorbing or "trapping" evaporative emissions when the engine is shut off. Upon starting of the engine, the flow of filtered air through the charcoal canister purges the vapors therefrom such that the vapors are delivered to the intake system for combustion by the engine.
Unfortunately, vapor control systems incorporated into modern motor vehicles have become increasingly complex and expensive due to a number of critical design requirements. First, the fuel filling system must prevent leakage of fuel and vapors during both refueling and normal operation of the vehicle. In addition, the fuel filling system must allow for the entry of air to replace the fuel within the fuel tank as it is consumed, and must also allow for venting of over-pressure conditions within the tank. The fuel filling system must also provide means for actuating the automatic shut-off mechanism incorporated in fuel dispensing nozzles. Furthermore, the fuel filling system must inhibit the leakage of liquid fuel and vapors upon impact and during the occurrence of a "roll-over" accident. Finally, modern fuel filling systems must prevent the introduction of leaded fuels into the fuel tank of the vehicle.
Conventional fuel filling and vapor control systems permit pressurized fuel vapors present within the motor vehicle fuel system to escape to the atmosphere upon removal of the fuel cap. It will be appreciated that a significant quantity of otherwise combustible fuel is lost to the atmosphere each time a vehicle is refueled. In addition, new fuel vapors are continually generated during refueling due to splash and agitation of the dispensed fuel, as well as from extreme temperature differences between the fuel in the fuel tank and the newly dispensed fuel. Furthermore, as liquid fuel is delivered into the fuel tank, fuel vapors are displaced from the fuel tank's vapor space and are typically released directly into the atmosphere through the fuel tank filler neck.
Another drawback associated with most conventional fuel filling systems is that over-filling of the fuel tank is not monitored and regulated. If the nozzle shut-off mechanism fails to terminate delivery of liquid fuel into the fuel tank, fuel will eventually back-up the fill pipe and spill onto the ground for alerting the operator to manually shut-off the nozzle. However, such over-filling of the fuel tank displaces the required "vapor dome" located above the desired maximum fill level of the fuel tank which can potentially cause fuel leakage during vehicle operation and/or contamination of the activated charcoal canister. In addition, lack of an adequate "vapor dome" within the fuel tank can also cause excessively high tank pressures due to extreme variations in the fuel temperature and volatility.